Hello. You indicated 100 feet wide, but how long and tall is this machine?
Couple of things that may be helpful. In a multi path environment, diversity is essential. You indicated that your access points can do diversity, which is good. Nothing says you cannot do diversity with splitters - each antenna port connects a 2-way splitter, each splitter sends a run of leaky coax left and right, both runs of coax separated 4 wavelengths apart. The insertion loss is clearly acceptable as you have already indicated.
What hasn't received much attention here is the clients. First, you indicated these travel in a horizontal plane - but where on the car is the antenna mounted? Is it feasible to relocate the antenna to the top of the car? Also, what are the specifications for the dipole antenna?
Something else - 180 clients in a 100W' x ?L' x ?T' piece of space likely qualifies as high-density. What is the client transmit power at? 180 clients chattering away at 100mW can cause a seriously high noise floor and excessive self-interference. They ought to be dropped to 1mW as well.
This machine... is it feasible to mount radio(s) in the interior?